Phase 6b/7b: per-child decoded periods, separate brief blocks, idempotent calendar (AUD-119)

- Parse each child's own "Today" day widget for the timetable (FR-16); drop the
  school-wide week calendar's lesson grid and clean the leaked routine rows.
- Add the editable codes map (FR-17): subjects, rooms, teachers and period
  labels, seeded, an unknown code falls back to the raw code; `school codes` CLI.
- Brief: Finn's block first, then Harry's, four sections always present (FR-9);
  periods decoded into plain English; the undated tail is one counted line (FR-18).
- Calendar: write periods + work due + work overdue + major events, per child,
  on every pass. Identity is the stable per-item key, so a re-run never re-inserts
  (FR-8). morning-brief.sh now runs scan -> calendar push -> notify.
- Day-widget labels are 12-hour: 1-6 read as PM, fixing afternoon periods.

Proven live on .13: image 0.6.2-phase6b7b; both children's briefs decoded and
separate; 35 events in calendar.school; runs 2 and 3 of the scan added nothing.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/decode/decode.go

@@ -0,0 +1,84 @@
+// Package decode turns a raw Compass lesson label into plain English using the
+// editable codes map (AGENTS.md §4 FR-17). An unknown code renders as the raw
+// code, never blank.
+package decode
+
+import (
+	"strings"
+	"unicode"
+
+	"gitea.lab.audasmedia.com.au/sam/compass_teams_nhs/internal/period"
+	"gitea.lab.audasmedia.com.au/sam/compass_teams_nhs/internal/store"
+)
+
+// Period renders one lesson title as plain English, for example
+//
+//	"1 - 7SCF - H14LAB - KNI" -> "Period 1 — Year 7 Science — Room H14LAB — Mr KNI"
+//
+// A title that is not a lesson (a concert, an excursion) is returned unchanged.
+// A code that is not in the map falls back to the raw code (FR-17).
+func Period(title string, m store.CodeMap) string {
+	slot, subject, room, teacher, ok := period.Split(strings.TrimSpace(title))
+	if !ok {
+		return strings.TrimSpace(title)
+	}
+
+	parts := make([]string, 0, 4)
+	parts = append(parts, periodName(slot, m))
+	if subject != "" {
+		parts = append(parts, codeName(m, store.CodeSubject, subject))
+	}
+	if room != "" {
+		parts = append(parts, codeName(m, store.CodeRoom, room))
+	}
+	if teacher != "" {
+		parts = append(parts, teacherName(m, teacher))
+	}
+	return strings.Join(parts, " — ")
+}
+
+// teacherName decodes a teacher field. Compass sometimes carries several codes
+// in the one field ("GT SMH"), so every token is decoded and joined.
+func teacherName(m store.CodeMap, field string) string {
+	tokens := strings.Fields(field)
+	if len(tokens) <= 1 {
+		return codeName(m, store.CodeTeacher, field)
+	}
+	out := make([]string, 0, len(tokens))
+	for _, tok := range tokens {
+		out = append(out, codeName(m, store.CodeTeacher, tok))
+	}
+	return strings.Join(out, " / ")
+}
+
+// periodName renders the period slot: a word label such as "C" uses the map
+// ("Connect"), a number becomes "Period 3", and anything unknown stays raw.
+func periodName(slot string, m store.CodeMap) string {
+	if name := strings.TrimSpace(m.Lookup(store.CodePeriod, slot)); name != "" {
+		return name
+	}
+	if isNumber(slot) {
+		return "Period " + slot
+	}
+	return slot
+}
+
+// codeName returns the mapped name, or the raw code when it is not mapped.
+func codeName(m store.CodeMap, kind, code string) string {
+	if name := strings.TrimSpace(m.Lookup(kind, code)); name != "" {
+		return name
+	}
+	return code
+}
+
+func isNumber(s string) bool {
+	if s == "" {
+		return false
+	}
+	for _, r := range s {
+		if !unicode.IsDigit(r) {
+			return false
+		}
+	}
+	return true
+}